New research shows that our body chooses which microorganism can live in our gut.

The human gastrointestinal (GI) tract is home to about 100 trillion symbiotic bacteria, which, seen from their DNA content, amount to more than 150 times the number of genes in the human genome. But, don't worry, many of these GI tract bacteria have beneficial functions. Beneficial gut bacteria ally with your intestinal cells to break down indigestible plant fibers, they also help your immune system protect itself against viruses, and increase intestinal absorption of dietary fats and carbohydrates.

Now, new research led by Dr. Jonas Schluter and Dr. Kevin Foster, from the Department of Zoology and the Centre for Integrative Systems Biology at the University of Oxford, United Kingdom, shows that we actually have a say on which bacteria survives in our guts. The report, published  in the November 20 issue of PLoS Biology, concluded that certain chemical secretions produced by intestinal epithelial cells, can influence which bacteria can leave the inside of the gut and move into other tissues.

The research team simulated the growth of different strains of bacteria on or near a host epithelium. Chemicals produced in areas closest to the epithelial cell layer determined which bacteria survived, and which did not. Bacteria found in areas of low concentration of these chemicals did not fare as well as those found in areas rich in these chemicals. These chemicals were present at lower amounts on the inside of the gut, opposite the epithelial surface, where extinction of the slower growing, beneficial types of bacteria, occurred in merely a few generations.

A similar case occurs in mammalian cells that produce attachment factors called glycoconjugates, which provide a "foothold" for the helpful Bacteroides thetaiotaomicron, so it can convert complex carbohydrates into forms that the host can use for energy. The discovery also has wider implications, as it may shed light on other host-microbe interactions such as those involving mucopolysaccharides growing on corals that regulate microbes growing on the coral's surfaces.

Image by Gerd Altmann